The earliest described immunization attempts were carried out in China over 900 years ago, where intranasal inoculation of dried and ground smallpox pustules was performed. In the classical immunology and in combination with vaccination against different types of infectious agents e.g. bacteria, virus or parasites the prevailing dogma has been to administer the vaccine subcutaneously or intramuscularly. However, research has during the last years shown that the body has a very effective immunological system that resides in the mucosa. It has also been shown that you can administer vaccines nasally, orally, rectally and vaginally. In the same way as for the classical immunization it has been shown that by mucosal vaccination there is also a need for enhancement of the immunological response by the addition of adjuvants.
The intranasal route has attracted increased attention because of the greater efficacy in inducing mucosal immune responses than the more conventional regimes of parenteral immunization. Furthermore, the realization that approximately 80% of the immune system reside in the mucosa combined with the fact that an equal percentage of the known pathogens enter our bodies via the mucosal membranes has pushed the interest towards the application of mucosal immunization.
It has also been shown that parenteral vaccines do not induce immune response at mucosal sites. Thus, it is also clear that appropriate stimulation of a mucosal site such as the nose or the gut, can generate immune response at other mucosal sites. As an example, it is possible to apply a vaccine in the nose and obtain an immune response in the vagina. Furthermore, the mucosal immune response is very rapid with onset only hours after being subjected to stimulation by a pathogen, as compared to parenteral immunity having a response time of several days.
Tuberculosis (TB) is one of the major causes of morbidity in the world with an estimated death toll of approximately 3 millions per year. It is estimated that ⅓ of the world's population is infected with TB. To a large extent TB is essentially an uncontrolled problem despite the use of the Bacille Calmette-Guérin (BCG) vaccine for more than 75 years.
The BCG vaccine consists of a weakened strain of tuberculosis bacteria taken from a cow in 1908. The original bacteria used today were cultured for 13 years for the purpose of weaken their pathogenic characteristics in order to be used as live bacteria for parenteral vaccination of humans. Basically the same strain is used today as the only vaccine available against TB. Several pharmaceutical companies around the world produce the BCG vaccine. The BCG formulation used today consists of freeze-dried attenuated viable BCG vaccine in one container and another container with physiologically acceptable suspension media. Before administration, the freeze-dried BCG is suspended and subsequently administered by injection to the patient. This procedure which has to be carried out immediately in connection with the vaccination, requires skilled personnel and decent facilities in order to avoid contamination. Unfortunately these criteria are hard to keep up with in the developing countries. Thus, it is estimated that failure to keep to this standard costs about USD 500 millions each year world wide. Consequently, huge savings could be made both in money and product safety, if a system was available where no mixing of vaccines was needed and where injections could be eliminated, thus eliminating the need for highly skilled personnel and sterile conditions.
In clinical trails around the world, the protective efficacy of the BCG vaccine has been shown to vary between −50% to +80%. This means that certain clinical studies have shown that in fact you enhance instead of diminish your risk of getting the disease after vaccination.
The BCG vaccine works well for children but has more or less no effect on adults. Consequently there are great efforts made in order to achieve a vaccine against TB for the grown-up population. Up to date however, there are no reports in the literature of a TB vaccine that is better than BCG.
Tuberculosis is spread by close person-to-person contact through infectious aerosols. On rare occasions the disease can be acquired by ingestion or skin trauma. This means that the first organ to get into contact with the bacteria during a normal infection is the mucosal surfaces in the lungs.
Adjuvants are a heterogeneous group of substances that enhance the immunological response against an antigen that is administered simultaneously.
Almost all adjuvants used today for enhancement of the immune response against antigens are particles or are forming particles together with the antigen. In the book “Vaccine Design—the subunit and adjuvant approach” (Ed: Powell & Newman, Plenum Press, 1995) almost all known adjuvants are described both regarding their immunological activity and regarding their chemical characteristics. As described in the book more than 80% of the adjuvants tested today are particles or polymers that together with the antigens (in most cases proteins) are forming particles. The type of adjuvants that are not forming particles are a group of substances that are acting as immunological signal substances and that under normal conditions consist of the substances that are formed by the immune system as a consequence of the immunological activation after administration of particulate adjuvant systems.
Using particulate systems as adjuvants, the antigens are associated or mixed with or to a matrix, which has the characteristics of being slowly biodegradable. Of great importance using such matrix systems are that the matrices do not form toxic metabolites. Choosing from this point of view, the main kinds of matrices that can be used are mainly substances originating from a body. With this background there are only a few systems available that fulfill these demands: lactic acid polymers, poly-amino acids (proteins), carbohydrates, lipids and biocompatible polymers with low toxicity. Combinations of these groups of substances originating from a body or combinations of substances originating from a body and biocompatible polymers can also be used. Lipids are the preferred substances since they display structures that make them biodegradable as well as the fact that they are the most important part in all biological membranes.
Lipids are characterized as polar or non-polar. The lipids that are of most importance in the present invention are the polar lipids since they have the capacity to interact and form particulate systems in water. Another way of defining these lipids are as amphiphilic due to their chemical structure with one hydrophobic and one hydrophilic part in the molecule thereby being useable as surface active substances. Examples of main groups of polar lipids are mono-glycerides, fatty acids, phospholipids and glycosphingolipids. These main groups can be further characterized depending on the length of the acyl chain and the degree of saturation of the acyl chain. Since the number of carbon atoms in the acyl chain can be in the range of 6 to 24, and the number of unsaturated bonds can be varied, there is an almost infinite number of combinations regarding the chemical composition of the lipid.
Particulate lipid systems can be further divided into the different groups as discussed in the scientific literature such as liposomes, emulsions, cubosomes, cochleates, micelles and the like.
In a number of systems the lipids may spontaneously form, or can be forced to form, stabile systems. However, under certain circumstances other surface-active substances have to be introduced in order to achieve stability. Such surface-active systems can be of non-lipid character but possess the characteristics of the polar lipids having hydrophobic and hydrophilic parts in their molecular structure.
Another factor that has been shown to be of importance is that lipids exhibit different physical chemical phases, these phases have in different test systems been shown to enhance uptake of biological substances after administration to mucous membranes. Examples of such physical chemical phases described are L2, lamellar, hexagonal, cubic and L3.
In the same way as within the classical immunology where vaccines (antigens) are administered parenterally, there is within mucosal immunization a great interest in directing the immunological response towards development of humoral and/or cellular response. If you obtain a humoral response it would be important to direct the response in a way that a certain class of antibodies would be obtained. In order to obtain such a goal, specific immune stimulating agents can be added to the formulation of antigens and adjuvants.
A formulation which fulfils these goals is described in PCT/SE97/01003, the contents of which is incorporated herein by reference. The disclosed formulation comprises monoglycerides and fatty acids. The monoglycerides comprise one or more substances selected from monoglycerides wherein the acyl group contains from 6 to 24 carbon atoms, preferably 8 to 20 carbon atoms, even more preferably 14-20 carbon atoms and where the acyl chain may contain unsaturated bonds.
The acyl chain of the fatty acid may be varied between 4 and 22, preferably 8 to 18 and where the acyl chain may contain one or more unsaturated bonds. A combination of the monoglyceride mono-olein and oleic acid has shown to be an L3 phase, which can be described as sponge-like structure, in contrast to liposomes that form onion-like lamellar structures.
Said combination of monoglycerides and fatty acids my be further formulated by the addition of a biocompatible and biodegradable oil thus forming an oil in water (o/w) or w/o/w emulsion. Such emulsions have been shown in the literature to be very effective in enhancing the cellular response against an antigen after administration to an animal (Singh, M., et al 1997, Vaccine 15, 1773–78). It is generally accepted that in order to have an acceptable vaccine against TB there is a need for a cellular immune response.